Off shore wind energy installation foundation system

ABSTRACT

The invention relates to a marine structure comprising a foundation system with three or more suction buckets. The suction buckets are designed to be installed in the seafloor to operate as a foundation or part of it to support an offshore structure resting onto the seafloor. The suction buckets support a connector body and the connector body is designed to support a payload. The invention also relates to a method of installing a suction bucket. During the method, the suction bucket bottom penetrates the seafloor and fluid is removed from the suction space such that penetration proceeds by suction.

The invention relates to a foundation system for an offshore payload,preferably an offshore wind energy installation, however also applicableto oil or gas applications. The foundation system is provided with threeor more suction buckets (hereafter also called “bucket”). The foundationsystem is in particular designed for the next generation off shore windenergy installations of 9 MW and higher. Particularly the foundationsystem is designed for supporting a single upright mast (also calledpole or post) which supports the payload, preferably at its top end. Incase of a wind energy installation the mast preferably comprises anupright monopole and on top of it an upright tower, wherein the towersupports the nacelle at its top. In stead of a nacelle the payload couldcomprise a platform, e.g. for oil or gas application. The mast, monopoleand tower are preferably a single tube and/or made of steel howeverreinforced mineral cement concrete is also feasible. The payloadpreferably will be located high above the sea, e.g. at least 10 or 20metre. Sea depth typically will be at least 10 or 20 or 50 metre.

Suction buckets and how to install them are a.o. known from GB-B-2300661and EP-B-0011894, which are enclosed in here by reference. Briefly, asuction bucket is a thin walled steel sleeve or pipe or cylinder, whichcylinder is closed at its longitudinal top end by a bulkhead (alsocalled top plate) or different sealing means and which cylinder issealingly located on the subsea bottom with the open end opposite thebulkhead since this open end penetrates the subsea bottom due to theweight of the suction bucket. Thus the cavity, also called suctionspace, delimited by the cylinder and the bulkhead is sealed by thesubsea floor such that vacuum or suction can be generated by removingwater from within the suction space such that a resulting force tends toforce the suction bucket deeper into the subsea floor. The creation ofthe suction can be with the aid of a suction source, such as a pump,being on, or close to or at a distance from the suction bucket andconnected to the suction space. The applied level of the suction can bee.g. at least substantially constant, smoothly increase or decrease orelse pulsate, for which there are convenient means. After use, thesuction bucket can easily be removed by creating an overpressure withinthe suction space, e.g. by pumping in (sea) water.

A self installing marine structure, e.g. platform applying suctionbuckets is known from e.g. WO99/51821 (SIP1) or EP-A-1 101 872 (SIP2) ofthe present inventor. WO 02/088.475 (SIP3) discloses a tower carrying awind turbine at the top and suction buckets as foundation.

Suction buckets are more and more applied as (part of) a foundation ofan off shore wind energy turbine. For such application, typically threeor more mutually spaced suction buckets are applied, providing a staticbalanced (in case of three suction buckets) or overbalanced (in case ofmore than three suction buckets) support. In operation, the suctionbuckets have at least almost completely penetrated the sea bed, are atequal or substantially equal level and have a mutual horizontal spacingproviding a clearance of at least 5 metre, typically in the order of 20metre, or a clearance of at least 0.5 or 1.0 times the diameter of thesuction bucket (clearance means the shortest distance between the facingside walls). This assembly of suction buckets carries a single monopoleor a space frame (also called jacket) of steel beams or tubes and on topof it a vertical tower supporting at its upper end the nacelle of thewind energy turbine provided with rotor blades, typically rotatingaround a horizontal axis and driven by the wind. The wind energy turbineconverts wind energy into electrical energy. The wind turbine istypically part of a wind farm of identical wind turbines each providedwith its own foundation of three or more suction buckets. A cable brings30 the electricity from the wind turbine generator to an electricityconsumer on shore, e.g. a household.

One of the benefits of suction buckets is that a marine structure can bedesigned to be self bearing and/or self installing by providing it withone or more suction buckets. So the hoisting device and the plant forinstalling the foundation, e.g. hammering device, can be eliminated.

Since the structure is provided with one or more suction buckets,removal (also called decommissioning) after use is made easier in thatby pressing out the suction bucket, the anchoring of the structure tothe underwater bottom can be removed. The structure is typically atleast substantially made from metal, typically steel.

Preferably each suction bucket has one or more of: a diameter of atleast 5 metres, typically between 10 and 15 metre or even more; a heightof at least 5 metres, typically between 10 and 15 metre or even more,subject to the soil conditions; a wall thickness of at least 1centimetre, typically at least 3 or 5 centimetre; the longitudinal axisof the suction bucket and the relevant supporting leg (of the upperstructure to be supported by the suction bucket) are substantially inline or eccentric.

OBJECT OF THE INVENTION

Particularly for wind energy turbines there are stringent requirementson many topics. Examples of these topics are: verticality of the towerfor the complete service life (typically 20 years) of the structure;vibration frequency; low production costs; environmental friendly;efficient recovery of verticality to repair a failure.

For verticality, typically, a deviation of more than 1 degree from thevertical will result in a seizure of the wind turbine operation, whichcould lead to penalty claims. Such deviation can occur at any timeduring the lifetime of the structure, e.g. caused by settlement of thesoil underneath or near the suction buckets, excessive forces from seawaves or the wind.

As an example for the vibration frequency topic, the design must be suchthat vibrations generated during operation may not lead to structuraldamage to the offshore structure. Natural frequencies play an importantrole in this respect. Resonance is preferably avoided.

The object of the invention is versatile and can be learned from theinformation disclosed in the application documents.

The present inventor has developed, in a preferred embodiment, asolution to this object embodied by a foundation system for an offshorewind energy installation, having one or more of the following: N, beingat least three, suction buckets at the corners of an imaginary,preferably regular, polygon, seen in top view; a round or polygonalconnector body, seen in top view, which preferably has at least Nradially external corners and supports the payload, e.g. the tower ofthe wind energy installation, preferably at its centre, and which is, ateach of N corners, connected to the top end of a relevant suction bucketby rigid connections, such that all N suction buckets are rigidlyconnected to the connector body; the connector body is providedcompletely below sea level and/or has a hollow monocoque structure orload bearing skin, possibly providing radial stays and/or being non rubelike; the connector body being of closed profile for its completeextension, preferably without any slits and/or having an impermeableskin; the cross section of the connector radially towards the outsidenarrows in height (i.e. axial direction of suction bucket) and/or width(i.e. tangential direction); the vertical distance between a suctionbucket or its top plate and the connector body is less than 5 or 2 or 1metre, more preferably less than 25 centimetre. The invention is alsodefined in the claims.

Thus, the upper structure comprising the mast or monopole and/or toweris supported by the connector body and the connector body is supportedby the suction buckets. In different words, the upper structure restsupon the connector body and the connector body rests upon the suctionbuckets.

Preferably one or more of the following applies to the connector body:comprises a centrally located tower or monopole receiving element; isdesigned to be or is filled with ballast material, preferably for atleast 50% of its enclosed volume; is made of steel or reinforced mineralcement concrete; is thin walled; transfers all the loads (includingvertical and horizontal loads, bending moments and torsion) from themonopole and/or tower to the suction buckets; is compact in height, e.g.to allow fabrication in a shop, which preferably does not exceed 1.5times the outer diameter of the prismatic part of the monopole and/ortower; a width such that, seen in top view, the foundation systemprovides an envelope having a maximum span measuring at least 3 timesthe outer diameter of a suction bucket; overlaps, seen in top view, withthe suction buckets and preferably does not radially extend beyond thesuction buckets; extends substantially horizontal or at an angle of lessthan 10 or 20 degrees with the horizontal; substantially box shaped;made from flat sheets; one or more of side face, upper face and lowerface are substantially flat and/or make corners where they mutually joinand/or are locally provided with stiffeners, preferably inside; has anangular cross section, at least for its arms; is present above the topplate of the suction buckets; is free from the sea bed; keeps a gap withthe sea bed of at least 25 or 50 centimetre; its arms have a height,preferably measured at their location of maximum height, at least 0.5 or0.6 or 0.75 and/or less than 1.5 or 2 or 2.5 times the diameter of themonopole at the level of the connector body; its arms have a width,preferably measured at their location of maximum width, at least 0.25 or0.5 and/or less than 1.0 or 1.5 or 2 times the height, preferablymeasured at their location of maximum height, of the arms; issubstantially star or triangular or square shaped as seen in top view;has a wall thickness at least 2 or 5 or 10 millimetre and/or less than200 or 100 or 50 millimetre; has a substantially flat lower side. Thearm is the member extending from the central part towards a bucket.

The invention is based on the discovery, made by the inventor, that oneor more or all the stringent requirements can be fully met by keepingthe foundation system as deep as possible below the water level,preferably below 10 or 15 meters above the seabed. Thus the mast ormonopole or tower must be as long as possible.

The invention is also based on the teaching, obtained by the inventor,that one or more of the following is possible: tilting correction; easeof transport over water to the final offshore destination; deeperpenetration of the suction buckets into the sea bottom; locating ballaston top of the suction buckets; minimizing pumping effect caused bycyclic loading of bucket top plate by the payload.

For the mast/monopole/tower one or more of the following applies: thelower part connecting to the connector body has an enlarged diameter,e.g. diameter 10 or 12 metre compared to 6.5 metre at the prismaticpart; diameter at water level at least 1 or 2 metre smaller than at thelevel of the connector body; wall thickness at least 20 or 35 millimetreand/or less than 200 millimetre, e.g about 50 millimetre; hollow; thinwalled; cylindrical for substantially its complete height; above thelevel of the upper face of the suction bucket top plate or the underside of the connector body.

The prior art shows many proposals for a foundation system for a mast ormonopole or tower. Examples are: WO2012103867A1 (Weserwind) discloses abelow sea level extending tripod type foundation for off shore windenergy application using three into the sea bed rammed piles;EP2558648B1 (Siemens) discloses another tripod type for off shore windenergy application using three into the sea bed rammed piles;EP1805414B1 (Bard Engineering) discloses a from the sea bed to above sealevel extending tripile type for off shore wind energy application usingthree into the sea bed rammed piles, and also addresses the need foravoiding the natural frequency of the foundation being equal to therotor frequency to avoid resonance; U.S. Pat. No. 5,567,086A discloses abelow sea level extending tension leg type system for off shore oildrilling; EP1074663A1 discloses an into the ground embedded star typefoundation system for wind energy application using ground anchoringrods.

The in this application cited documents are inserted in here byreference and each provide technical background for a betterunderstanding of this invention.

After installation into the sea bed is completed, a gap (also called“void”) can remain between the top of a soil plug inside the suctionspace and the closed suction bucket top. For wind turbine applications,such gap needs be filled with filler material or a filler body toprevent settlement of the suction bucket and to transfer the loads, e.g.downward or shear, from the wind turbine and structure in to the seabed.It is feasible that this filler material cures or hardens or becomesrigid after it has entered the gap. This filler material provides a body(hereafter also called “slab”) inside the suction space. Obviously, thisslab is typically provided after the suction bucket is sunk to the waterbottom and penetrated the water soil to its final depth, by pouring orcasting the at that time flowable material of the slab into the seawater filled space between the top bulkhead and the top face of the soilplug within the suction bucket.

This slab typically has a height of at least 10 or 20 or 30 centimetresand/or less than 50 or 100 or 150 centimetres.

It is noted that the invention is preferably directed to suction bucketsfor foundations, in other words designed to carry the weight of an upperstructure, e.g. wind turbine or platform, placed on top, to avoid thatsuch upper structure sinks into the subsea bottom. Thus a foundationsuction bucket bears loads from the associated upper structure whichtend to force the suction bucket further into the ground. The slab belowthe top bulkhead is designed to prevent that the suction bucket movesdeeper into the subsea bottom due to the pushing loads generated by theweight of the upper structure. A foundation suction bucket is by thenature of its loading different from a suction bucket for anchoring,which anchoring suction bucket must withstand pulling forces from theanchored object which tries to leave its desires location by trying topull the anchoring suction bucket out of the subsea bottom.

Preferably one or more of the following applies: the suction required topenetrate the suction bucket into the subsea bottom during installationand/or the overpressure applied during settlement correction or toextract the suction bucket from the sea bed is generated within thesuction bucket above the slab or above the top bulkhead of the suctionbucket, preferably since the suction side of a suction pump means or thepressure side of a pressure pump means is connected to the suctionbucket at a location above the slab, e.g. the top bulkhead is providedwith a nozzle or different sealable port for fluid connection of thesuction space with a suction or pressure pump means; the diameter of thesuction bucket is constant over its height (the height is the directionfrom the top bulkhead towards the opposite open end); from the topbulkhead the cylinder walls of the suction bucket extend parallel; theopen end of the suction bucket, designed to be located on the sea floorfirst is completely open, in other words, its aperture is merelybordered by the cylinder walls; the water depth is such that the suctionbucket is completely below the water surface when its lower end contactsthe sea floor, in other words when its lower end has not penetrated thesea floor yet; the foundation comprises three, four or more mutuallyspaced suction buckets; the slab completely fills the gap; with thepenetration of the suction bucket into the sea floor completed, the topbulkhead is spaced from the sea floor and/or the lower side of the slabbears onto the sea floor which is possibly at elevated level within thesuction bucket, compared to the seafloor level external from the suctionbucket, due to raising of the seabed plug within the suction spacecaused by penetration of the suction bucket into the seabed; the byreleasable sealing means, e.g. a valve, selectively closable port in thetop bulkhead to allow water entering and/or exiting the suction bucketis provided with a coupling means designed for temporary engagement of asuction and/or pressure pump at the time of installing, settlementcorrection and removing, respectively, of the suction bucket into andfrom, respectively, the seafloor soil, which port is associated with thefluid flow channel.

Preferably, the design of the suction bucket is such that fluid from asource, e.g. pressure pump, flows from the source through a sealedchannel, terminating below the bulkhead and within the suction space.During sucking in the pressure is typically at least 0.1 or 0.25 or 0.5or 1 bars below the local water pressure external from the suctionbucket. During pressing out (correction operation or decommissioning)the pressure is typically at least 0.25 or 0.5 or 1 or 2 bars above thelocal water pressure external from the suction bucket.

The suction bucket is also preferably provided with known as such valvesand/or hatches adjacent or at its top bulkhead for selectively allowingwater and air to enter or exit the suction space through the top side ofthe suction bucket.

Preferably the invention is directed to an offshore foundation system ora suction bucket of said system, the suction bucket preferably providedby an open bottom and closed top, advantageously cylindrical, elongateshell providing a suction compartment or suction space, said closed tophaving an externally facing upper face and an opposite, toward thesuction space facing lower face and preferably provided with one or morevalves selectively allowing fluid communication between the suctionspace and the environment, the suction space being provided with afixedly located slab and wherein, in use, the slab bottom bears ontoatop of a soil plug inside the suction space, the top bulkhead of thesuction bucket bears onto the slab.

A possible procedure is as follows: the foundation system provided withat least three suction buckets is installed and when the buckets havearrived at their final penetration depth into the sea bed, e.g. of sandor clay, the slab, if applied, is provided by introducing the flowablefiller material such that the gap is completely or substantially filled.Subsequently the upper structure to be supported by the foundationsystem is installed. First, the monopole is located on top of thefoundation system, followed by installing the tower on top of themonopole. The tower carries the wind energy turbine nacelle at its topend. The tower is completely or partly above water level.

The ballast material applied preferably has a specific weight of atleast 1,400 (e.g. sand) or 2,000 (e.g. rock) kg per cubic metre, thus atleast 1.4 times or twice the specific gravity of water. In an embodimentthe ballast is concentrated near the suction buckets, e.g. located ontop of the suction buckets. The ballast can have a thickness of at least1 or 1.5 or 2 metres. Application of ballast to the connector bodyand/or the suction buckets is also feasible.

The connection between connector body and monopole can be provided bygrouting or welding or mechanical fastening means, e.g. riveting orbolting. Use of a quick coupling is preferred, e.g. of so called slipjoint type, such as disclosed in EP 2 910 686 (KCI the engineers,disclosed in here by reference) and to which claim 14 is directed.

A quick coupling of slip joint type is preferably provided (see alsoFIG. 15) by wedging walls inclined at a sharp angle relative to theaxial direction of the tower and located at the tower and/or connectorbody at locations where the tower penetrates into the connector body, orvice versa, and oriented such that said wedging walls extend outwardfrom the tower, as viewed in upward direction of the tower in its finalvertical attitude as installed, such that the wedging walls provide aconical shaped circumferential or peripheral, e.g. ring like, means, afirst one at the tower, a second one at the connector body andconfigured such that if the tower and connector body are mutuallypenetrated or inserted, the wedging walls of the first and second onemutually engage and contact, retaining the tower against furtherlowering by gravity action and also generating radially inward directedclamping forces between these wedging walls, keeping the tower clampedto the connector body. The first one and the second one make a pair andpreferably there are two pairs, mutually spaced axially of the tower, atleast 0.5 meter.

The words “mast”, “monopole” and “tower” have individual meaning,however also identical meaning, e.g. more general, such as: each beingan elongated tube or pole like object. Thus, if any of these three wordsis used in this disclosure, it can also have a meaning identical to anyof the two other of these three words and/or the more general meaning.

The invention is further illustrated by way of non-limiting, presentlypreferred embodiments providing the best way of carrying out theinvention and shown in the drawings.

FIG. 1A-C show a first embodiment from three different angles; FIG. 2-4show a perspective view of a second, third and fourth embodiment,respectively; FIG. 5A-C show a perspective view, of exploded type, ofthree alternative ways of mounting the monopole to the foundationsystem; FIG. 6-8 show in side view the three main phases during apossible manner of installing the off shore wind energy installation;FIG. 9-14 show prior art foundation systems; FIG. 15 shows a double slipjoint in section from the side.

FIG. 1 shows three suction buckets, on top of it a star schapedconnector body having three arms, each radially outward converging, andthere above a single upright tube providing a mast and/or tower and/ormonopole. The lower part of the mast has a conical shape.

FIG. 2 shows three suction buckets, there above a triangular shapedconnector body and there above a prismatic mast. The water level 100 isalso illustrated. FIG. 3 shows four suction buckets, a star shapedconnector body having tour arms and above it a prismatic mast. FIG. 4shows a scar shaped connector body having three arms and a prismaticmast.

In FIG. 5A the lower end of the mast penetrates the connector body. InFIG. 5B the lower end of the mast penetrates a from the connector bodyupwards projecting transition piece. In FIG. 5C the transition piecepenetrates the lower end of the mast. In all three cases the slip jointcan be applied.

According to FIG. 6, the suction buckets and connector body provide asub assembly separate from the mast or tower or monopole. Thissubassembly was sailed to its final offshore location and there thesuction buckets were penetrated into the sea bed. After that part of themast was added (FIG. 7) and after that a further part of the mast wasadded (FIG. 8).

Different from FIG. 6-8, an alternative manner of installation is tosail the subassembly shown in FIG. 7 (buckets, connector body andmonopole mutually assembled at a remote location) to the final offshorelocation and install it there, after which the payload is added.

FIG. 9 shows a jacket type, FIG. 10 a tripod type, FIG. 11 a tripodtype, FIG. 12 a tri pile type, FIG. 13 a buried type and FIG. 14 atension leg type offshore structure.

Typically, there are three stages during penetration of the suctionbucket into the sea floor by suction within the suction space. In theinitial stage the open bottom of the suction bucket has penetrated theseabed by gravity, such that the suction space is sealed. The secondstage is obtained by removing water from the suction space by pumping,such that suction is created within the suction space such that thesuction bucket penetrates deeper into the seabed, thus its top comescloser to the seabed. In the third stage the suction bucket ispenetrated to its final depth, providing its design load bearingcapacity for a weight resting on top of it. Typically, the top bulkheadis spaced from the sea floor. Within the suction space internal from theside wall of the bucket, the surface of the sea floor material rises dueto penetration of the suction bucket. Such seabed part captive withinthe suction space is also called soil plug. Typically the void betweenthe bulkhead and the soil plug is tilled by a slab or body. The suctionspace is bounded by the top bulkhead, the cylindrical side wall and theopen end opposite the top bulkhead.

FIG. 15 shows an inner tube, e.g. the monopole, and an outer tube, e.g.the wall of the central hole of the connector body to receive themonopole. Each tube is provided with two axially spaced conical rings,providing two pairs of each an inner ring of the inner tube and an outerring of the outer tube. Due to the downward directed force Fv, orientedaccording to the gravity force, the radially inward directed clampingforces are generated (only shown for the upper pair).

The invention is not limited to the above described and in the drawingsillustrated embodiments. E.g. the marine structure can have a differentnumber of suction buckets. The drawing, the specification and claimscontain many features in combination. The skilled person will considerthese also individually and combine them to further embodiments.Features of different in here disclosed embodiments can in differentmanners be combined and different aspects of some features are regardedmutually exchangeable. All described or in the drawing disclosedfeatures provide as such or in arbitrary combination the subject matterof the invention, also independent from their arrangement in the claimsor their referral.

1-17. (canceled)
 18. Offshore structure that is provided with afoundation system with three or more suction buckets to be installed inthe seabed, which buckets are located at the corners of an imaginarypolygon, viewed in top view, to act as a foundation system or partthereof for carrying an offshore structure supported on the seabed, thesuction buckets carrying a connector body and the connector body adaptedfor carrying a payload.
 19. Offshore structure according to claim 18which is designed as an offshore wind energy installation of at least 9MW extending upwards from the seabed at an offshore location where theseabed is at least 50 meters below the local water level, and from thisinstallation runs a electricity cable to an electricity consumer on landto bring the offshore generated electricity to it.
 20. Offshorestructure according to claim 18, and with a star-shaped, seen in topview, connector body with the same number of external corners as thereare suction buckets, which external corners are formed by the radialoutwardly extending arms which provide the star shape; and with a singlevertical tower placed, centrally, between the suction buckets, seen intop view, formed by a single tube and made of thin-walled steel, whichcarries the gondola of the windmill at its top, the gondola with therotor blades at least 20 meters above the local water level. 21.Offshore structure according to claim 18, wherein the tower rests on topof the foundation system and the connector body rests on top of allsuction buckets; configured so that the foundation system is as deep aspossible below the water level and the tower has the largest possiblelength; the tower is located completely above the underside of theconnector body, is hollow and thin-walled with a wall thickness between20 and 200 millimetres and above the water level prismatic over itsentire length and is rigidly mounted to the connector body.
 22. Offshorestructure according to claim 18, wherein each suction bucket is avertical thin-walled steel cylinder with a wall thickness of at least 3millimetres and with a diameter between 10 and 15 meters, which at itstop end is closed in airtight manner by a top plate and at its lowerend, which is in fluid communication with the suction space inside thesuction bucket, is open and extends into the seabed with this lower endand is during installation in the seabed by hydraulic underpressuregenerated in the suction space inside the cylinder, generated by anexternal suction pump connected to an at the top plate provided suctionport with suction valve in fluid communication with the suction space,penetrated deeper into the seabed to be almost completely in the seabed;the suction buckets have a mutual spacing of at least 5 meters andprovide a statically balanced or overbalanced support for the connectorbody; each suction bucket contains a moulded filling body inside, withwhich after completion of the sucking, the gap between the top of theseabed inside the suction bucket and the top plate is completely filledup and which filling body has a height between 10 and 100 centimetresand prevents that the suction bucket is pushed deeper into the seabed bythe structure resting on top of it.
 23. Offshore structure according toclaim 18 wherein the connector body has arms which are the elementsextending from the central part of the connector body radially outwardlyto each relevant suction bucket and attached thereto at their ends; theconnector body has a flat underside and is a completely closed body andcompletely hollow and has a closed, thin-walled monocoque constructionwhose external walls carry the loads.
 24. Offshore structure accordingto claim 18, wherein the cross-section of the arms of the connector bodyis box-shaped with an angular cross-section and wherein the arms of theconnector body extend horizontal and are made from flat plates, and thefour flat sides, i.e. the top, bottom, left side and right side, of eacharm connect to each other via angular corners.
 25. Offshore structureaccording to claim 18, wherein the tower, the connector body and thesuction buckets are rigidly mounted so that all loads, includingvertical and horizontal loads, bending moments and torsion, aretransmitted from the tower to the suction buckets via the connectorbody; the attachment of the tower to the connector body is arranged as abeam of which a single longitudinal end is fixedly wedged so that thetower extends vertically upwards from the connector body as a cantileverbeam, in other words the tower is above the connector body free fromstructures that transfer mechanical loads from the tower onto theseabed.
 26. Offshore structure according to claim 18, wherein thefoundation system extends a maximum of 15 meters above the local seabedand is located completely below the highest point of the connector bodyand only in the area downwards from the highest point of the connectorbody extend structures that are to the tower attached and transfer allloads, from the tower to the seabed.
 27. Offshore structure according toclaim 18, wherein the arms of the connector body have a height, measuredat their location of maximum height, between 0.75 and 1.5 times thediameter of the tower at the level of the connector body and have awidth, measured at their location of maximum width, between 0.5 and 1.0times their height, measured at their place of maximum height. 28.Offshore structure according to claim 18, wherein the connector body andthe tower are equipped with one or more quick couplings which keep, asthe only means, the tower and the connector body together in a loadbearing manner, wherein the quick couplings allow uncoupling withoutcausing permanent damage to the parts involved in the coupling. 29.Offshore structure according to claim 28, wherein the complete forceflow from the connector body to the tower, and vice versa, flows for aminimum of 95% via the quick couplings.
 30. Offshore structure accordingto claim 28, wherein the one or more quick couplings provide a clampingof the tower in the connector body, or vice versa, by wedging action anddriven by the gravity force acting on the tower, so that by moving ofthe longitudinal end of the tower clamped in the connector body due towobbling of the tower, the tower is increasingly tightly clamped to theconnector body.
 31. Offshore structure according to claim 28, whereinthe one or more quick couplings are each provided with one or two firstwedging means, e.g. conical rings, provided to the tower, that areconically or wedge shaped at one side and one or two second wedgingmeans, e.g. conical rings, provided to the connector body, that arewedge or conically shaped at one side, such that there are one or twopairs of each a first and a second wedging means such that when thequick coupling is engaged, by inserting the tower into the connectorbody or vice versa, the wedging means are co axial and parallel and thewedge or conical sides of the wedging means of a pair face and contacteach other, the first wedging means at the inner side or within thesecond wedging means, or vice versa, in case there are two pairs, thedistance between the two first wedging means rings equals the distancebetween the two second wedging means, viewed in longitudinal directionof the tower, wherein a pair provides a slip joint (see FIG. 15). 32.Method of installing the offshore structure according to claim 18,wherein a first sub-unit comprising the suction buckets and theconnector body and a second sub-unit comprising the tower are provided,and the first and second sub-units are subsequently, separate from eachother, at least 10 meters apart, floating in the water transported bysailing over a distance of at least 100 or 1000 meters to the offshoreinstallation location, with the first subunit in upright position, andthen the first and second sub-unit, floating in the water, are combinedinto the offshore construction.
 33. Method according to claim 32,wherein during the float transport in the water to the offshoreinstallation location, the first and the second subunit sail underneathone or more bridges, of a fixed type, for car traffic crossing the waterway, without obstructing the car traffic across the bridge.
 34. Methodaccording to claim 32, wherein the first subunit and the second subunitare combined by activating quick couplings at the connector body and thetower.
 35. Offshore structure that is provided with a foundation systemwith three or more suction buckets to be installed in the seabed, whichbuckets are located at the corners of an imaginary polygon, viewed intop view, to act as a foundation system or part thereof for carrying anoffshore structure supported on the seabed, the suction buckets carryinga connector body and the connector body adapted for carrying a payload;wherein the offshore structure is designed as an offshore wind energyinstallation of at least 9 MW extending upwards from the seabed at anoffshore location where the seabed is at least 50 meters below the localwater level, and from this installation runs a electricity cable to anelectricity consumer on land to bring the offshore generated electricityto the electricity consumer; the connector body is star-shaped, seen intop view, with the same number of external corners as there are suctionbuckets, which external corners are formed by the radial outwardlyextending arms which provide the star shape; and the offshore structureis provided with a single vertical tower placed centrally between thesuction buckets, seen in top view, formed by a single tube and made ofthin-walled steel, which carries the gondola of the windmill at its top,the gondola with the rotor blades is provided at least 20 meters abovethe local water level; the single vertical tower rests on top of thefoundation system and the connector body rests on top of all suctionbuckets; and the offshore structure is configured so that the foundationsystem is as deep as possible below the water level and the tower hasthe largest possible length; the tower is located completely above theunderside of the connector body, is hollow and thin-walled with a wallthickness between 20 and 200 millimetres and is above the water levelprismatic over its entire length and is rigidly mounted to the connectorbody; each suction bucket is a vertical thin-walled steel cylinder witha wall thickness of at least 3 millimetres and with a diameter between10 and 15 meters, which at its top end is closed in airtight manner by atop plate and at its lower end, which is in fluid communication with thesuction space inside the suction bucket, is open and extends into theseabed with this lower end and is during installation in the seabed byhydraulic underpressure generated in the suction space inside thecylinder, generated by an external suction pump connected to an at thetop plate provided suction port with suction valve in fluidcommunication with the suction space, penetrated deeper into the seabedto be almost completely in the seabed; the suction buckets have a mutualspacing of at least 5 meters and provide a statically balanced oroverbalanced support for the connector body; the connector body has armswhich are the elements extending from the central part of the connectorbody radially outwardly to each relevant suction bucket and attachedthereto at the ends of the arms are the suction buckets; the connectorbody has a flat underside and is a completely closed body and iscompletely hollow and has a closed, thin-walled monocoque constructionwhose external walls carry the loads; the cross-section of the arms ofthe connector body is box-shaped with an angular cross-section andwherein the arms of the connector body extend horizontal and are madefrom flat plates, and the four flat sides, i.e. the top, bottom, leftside, right side, of each arm connect to each other via angular corners;the tower, the connector body and the suction buckets are rigidlymounted so that all loads, including vertical and horizontal loads,bending moments and torsion, are transmitted from the tower to thesuction buckets via the connector body; the attachment of the tower tothe connector body is arranged as a beam of which a single longitudinalend is fixedly wedged so that the tower extends vertically upwards fromthe connector body as a cantilever beam, in other words the tower isabove the connector body free from structures that transfer mechanicalloads from the tower onto the seabed; the foundation system extends amaximum of 15 meters above the local seabed and is located completelybelow the highest point of the connector body and only in the areadownwards from the highest point of the connector body extend structuresthat are to the tower attached and transfer all loads, from the tower tothe seabed.